This invention relates to techniques, equipment and process unit operations for production of hydrocarbon fuels and low pour point distillate. The invention involves concurrent catalytic oligomerization of C.sub.5 + olefinic hydrocarbons with cracking and/or isomerization of lightly branched or normal paraffins in a waxy distillate to produce C.sub.5 + gasoline and low pour point distillate. More particularly, the invention involves the advantageous system integration of process units for simultaneous olefin oligomerization and distillate dewaxing into catalytic hydrocarbon cracking processes to permit the common utilization of product separation operations.
Reactor systems and processes for dewaxing petroleum distillates have been known for a long time. Dewaxing is, as is well known, required when highly paraffinic oils are to be used in products which need to remain mobile at low temperatures e.g., lubricating oils, heating oils, jet fuels. The higher molecular weight straight chain normal and slightly branched paraffins which are present in oils of this kind are waxes which are the cause of high pour points in the oils and if adequately low pour points are to be obtained, these waxes must be wholly or partly removed. Catalytic dewaxing processes are employed to selectively crack the longer chain n-paraffins to produce lower molecular weight products which may be removed by distillation. Processes of this kind are described in U.S. Pat. No. 3,668,113. (7.ANG.+), such as ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-48 and Zeolite Beta may be employed for this purpose. Medium pore zeolites, especially ZSM-5 (sometimes called "MFI"), have the preferred property of selectivity and their use forms the basis of the Mobil Distillate Dewaxing process ("MDDW"). The MDDW process is usually a fixed bed process that typically operates at 20 to 55 atm (2058 kPa to 5660 kPa), 260-430.degree. C. reactor temperature, and 40-70 m.sup.3 /b of hydrogen circulation.
U.S. Pat. No. 4,332,670 (Antal) discloses catalytic dewaxing of FCC light oil with ZSM-5 employing hydrogen recycle. U.S. Pat. No. 4,483,760 (Tabak et al) describes sequential fixed bed dewaxing of middle distillate with flash separation. U.S. Pat. No. 4,419,220 (LaPierre et al.) discloses fluidized bed dewaxing-isomerization of distillate fuel oil over zeolite Beta. U.S. Pat. No. 4,541,919 (LaPierre et al. discloses fluidized bed hydrodewaxing with ZSM-5. U. S. Pat. No. 3,891,540 (Demmel et al) discloses a combined process for catalytic cracking and distillate dewaxing using ZSM-5 catalyst. U.S. Pat. No. 4,181,598 (Gillespie et al) U.S. Pat Nos. 4,283,271 and 4,283,272 (Garwood et al) also describe the Mobil Lube and Distillate Dewaxing Process ("MLDW") using zeolite catalyst. The foregoing patents, of common assignee, are incorporated herein by reference in their entirety.
Conversion of olefins to gasoline and/or distillate product is disclosed in U.S. Pat. Nos. 3,960,978 and 4,021,502 (Givens, Plank and Rosinski) wherein gaseous olefins in the range of ethylene to pentene, either alone or in admixture with paraffins, are converted into a gasoline blending stock by contacting the olefins with a catalyst bed made up of ZSM-5 or related zeolite. In U.S. Pat. Nos. 4,150,062 and 4,227,992 (Garwood et al) discloses the operating conditions for the Mobil Olefin to Gasoline/Distillate ("MOGD") process for selective conversion of C.sub.3 + olefins. A fluidized bed process for converting ethene-containing C.sub.5 + olefinic hydrocarbonic streams, sometimes referred to as the Mobil Olefin to Gasoline ("MOG") process is described in U.S. Pat. Nos. 4,822,477; 4,873,385; '389 (Avidan et al); 4,855,524 and 4,859,308 (Harandi et al). The reaction phenomena of shape-selective polymerization are discussed by Garwood in ACS Symposium Series No. 218,Intrazeolite Chemistry, "Conversion of C.sub.2 -C.sub.10 to Higher Olefins over Synthetic Zerolite ZSM-5", 1983 American Chemical Society.
The olefins contained in an FCC gas plant are an advantageous feed for oligomerization. U.S. Pat. No. 4,090,949 discloses upgrading olefinic gasoline by conversion in the presence of carbon hydrogen-contributing fragments including olefins and a zeolite catalyst and where the contributing olefins may be obtained from a gas plant. U.S. Pat. Nos. 4,456,781, 4,831,203, '204, '205 (Owen, Tabak et al), disclose aspects of related oligomerization processes using an olefinic feedstock derived from FCC effluent.
The conventional MOG process design is concerned with converting light olefins (e.g., ethylene) in a fuel gas stream, such as an FCC off-gas, to gasoline. Motor octane of the gasoline produced is generally about 80-85. Typically, paraffins conversion under MOG process conditions is not significant.
It is an object of the present invention to provide a novel integrated reactor system for the simultaneous dewaxing of distillate fuel oil and the oligomerization of C.sub.5 + olefinic hydrocarbon to fuel products. Another object of the invention is to provide this system employing zeolite catalyst in a common conversion reaction zone. Yet another object of the invention is to integrate the foregoing process invention with catalytic or thermal cracking unit operations in order to utilize C.sub.5 + olefinic hydrocarbon and may utilize common FCC plant separation vessels.
Another object of this invention is to upgrade simultaneously a light olefinic FCC gas stream and waxy heavier distillate stream along with one or more of the following intermediate hydrocarbon streams: 1) benzene-rich streams, such as reformate C.sub.6 -rich heart cut; hydrotreated FCC or coker heavy naphtha; pyrolysis gasoline; and light straight run naphtha.